Gasification is a continuous thermal decomposition process in which solid organic or carbonaceous materials (feedstock) break down into a combustible gas mixture. The combustible gas components formed are primarily carbon monoxide (CO), hydrogen (H2), and methane (CH4). Other non-combustible gases such as nitrogen (N2), steam (H2O), and carbon dioxide (CO2) are also present in various quantities. The process of gasification involves pyrolysis followed by partial oxidation, which is controlled by injecting air or other oxygen containing gases into the partially pyrolysed feedstock. More specifically, biomass gasification is a sequence of reactions including water evaporation, lignin decomposition, cellulosic deflagration and carbon reduction. If concentrated oxygen is used, the resulting gas mixture is called syngas. If air (which includes nitrogen) is used as the oxidant, the resulting gas mixture is called producer gas. For simplicity, the term “producer gas” as used herein shall include both syngas and producer gas. Both gas mixtures are considered a “fuel gas” and can be used as a replacement for natural gas in many processes. They can also be used as a precursor to generate various industrial chemicals and motor fuels. When biomass is used as the feedstock, gasification and combustion of the producer gas is considered to be a source of renewable energy.
Producer gas may be burned directly in some engines and burners, purified to produce methanol and hydrogen, or converted via the Fischer-Tropsch and other methods and processes into synthetic liquid fuel.
Charcoal has been used to clean liquids and gases since as early as 2000-1500 B.C. As gas passes through activated carbon, the carbon absorbs many of the impurities as well as CO and CO2.
Microwaves have been used to heat substrates since the 1950s, with adoption of microwaves to catalyze chemical reactions beginning in the 1980s. Microwaves have the ability to heat a substrate without heating the surrounding vessel and also the ability to heat the inside of a substrate rather than simply heating the outside of it. Microwaves can also heat a substrate faster than traditional heating methods. Finally, it typically requires less energy to heat a substrate using a microwave than through conduction or convection.
Many devices and techniques have been used to purify, clean and prepare fuel gases, particularly syngas created as a result of gasification of biomass in the presence of concentrated oxygen and producer gas created as a result of gasification of biomass in the presence of air (which includes Nitrogen). In order for syngas or producer gas to be useful as a fuel gas, the tar and other contaminants must be removed from the gas.
Current devices and methods typically rely on partially combusting the unprocessed gas in order to generate the energy required to break down tars. These devices and methods waste the gas and may introduce additional contaminants as a result of incomplete combustion of tars.
What is needed is an efficient, low cost device and method to remove tars and other contaminants from unprocessed syngas and producer gas in order to prepare fuel gas. The device and method should not rely on combusting the gas as an energy source, but should rely on a lower cost energy source to complete the purification.